with a twin system you need 2 of almost every component, 2 turbos, 2 wastegates, 2 downpipes, etc. Assuming that you have a stock motor, like EatonUalive said, just go with a single, quick spooling turbo (for your car with the auto I would said something in the 66mm to 70mm range) and keep it simple. The car will be very fun with the built auto and a turbo!